The invention relates to a method and an arrangement for controlling the through flow of fluid material especially of venting gases and vapors in a tank-venting system of a motor vehicle having an engine and a fuel supply tank.
Furthermore, the invention relates to a corresponding through-flow control valve as well as a control unit for operating such an apparatus.
In motor vehicles, which are driven by internal combustion engines, a venting or aerating of the fuel supply tank is absolutely necessary for a trouble-free fuel flow. When fuel is consumed, air must be able to flow into the tank because otherwise a vacuum would form and the flow of fuel would become intermittent. The tank also has to be aerated to permit the contents of the tank to be able to expand when there is warming. In addition, when tanking, sufficient air must be able to exit from the tank so that the fuel added to the tank does not again bubble out of the fill stub.
In motor vehicles, tank venting systems are increasingly used wherein the vaporizing or excess fuel vapor is not conducted into the ambient but is directed via a venting line into an active charcoal filter. The fuel vapor or the fuel gas is there stored and is supplied during operation of the vehicle via a clocked controllable electromagnetic tank-venting valve to an intake manifold of the engine and therefore to the combustion. The maximum through flow in overcritical pressure relationships in the valve is mostly in the range of 3 to 6 kilograms per hour (kg/h). In this way, an emission of the environmentally-damaging fuel vapor from the tank into the ambient is substantially prevented and, at the same time, the fuel vapor, which is supplied to the engine, is itself utilized as fuel whereby the fuel consumption is significantly reduced at least from time to time.
In such tank-venting systems, the vapor quantity, which flows via the tank-venting valve, is varied, in most instances, in a controlled (open loop or closed loop) manner within pregiven limits in dependence upon the fuel concentration present at a particular time as well as on the then present rpm/load operating point of the engine. An adequately precise meterability of the vapor flow, which flows out via the tank-venting valve, must be guaranteed even for a comparatively low total air flow, which is inducted by the engine. Such a comparatively small total air flow takes place, for example, when the engine is operated at idle. So-called xe2x80x9cclocked valvesxe2x80x9d are preferably used as such valves.
A problem of the known clocked valves with the above-mentioned high throughput is a deficient small-quantity meterability. A through flow of approximately 0.2 kg/h can only be adjusted with a large tolerance of approximately +/xe2x88x920.1 kg/h. The reason for these large through-flow tolerances lies especially in the naturally occurring draw delay of the valves whose tolerance lies in the range of approximately +/xe2x88x921 millisecond (ms). The draw delay is the time duration between the electrical drive of the clocked valve and its mechanical opening.
The clock frequency of the valves is the frequency of an electrical drive signal of the clocked valve. This clock frequency of the valve should not drop below 8 Hertz (Hz) in order to especially avoid a defective time-dependent even distribution for the operation of the valve.
A short number comparison should make the relationships somewhat clearer. Assuming the above-mentioned tolerance of +/xe2x88x921 ms, with two valves with respectively different through flows (or maximum throughputs), a throughput of 0.12 kg/h should be attained. A clock frequency of 10 Hz is assumed for both valves. In one valve having a nominal throughput of 6 kg/h, a mechanical opening duration of the valve of 2 ms results which yields a through-flow tolerance of +/xe2x88x9250% for the assumed draw-delay tolerance. In contrast thereto, for a valve having a nominal throughput of 2 kg/h, a mechanical opening duration of 6 ms results and, therefore, a through-flow tolerance of comparatively only +/xe2x88x9216.6%. The opening duration or open time of a valve is defined as the time duration during which the valve is mechanically opened and a through flow can accordingly take place. The open time is the difference of the drive time and the draw delay already defined above.
With respect to the above tolerances, reference can be made to U.S. Pat. No. 5,873,350 which is incorporated herein by reference.
It is an object of the invention to provide a method and an arrangement of the kind described above wherein a meterability of the through flow as fine as possible for very low throughputs as well as for very high throughputs of fluid substances (gases, vapors, liquids, et cetera) is made possible. At the same time, the arrangement should be manufacturable and operable at favorable costs. The drive of such an arrangement should especially be possible with the least amount of technical complexity and not only with respect to a use in motor vehicles.
The method of the invention is for controlling the through-flow of fluid substances including venting gases and/or vapors in a tank-venting system of a motor vehicle having a fuel supply tank and an internal combustion engine. The method includes the steps of: generating a time-dependent clocked first through flow of a first through-flow amount; generating a time-dependent clocked second through flow with the first through flow being nominally less than the second through flow; and, switching in the second through flow at a time delay relative to the first through flow.
The method of the invention has the steps of generating a first time-dependent clocked through flow as well as at least a second time-dependent clocked through flow. The first through flow is nominally less than the second through flow and the second through flow is switched in delayed in time compared to the first through flow. For short drive times, the method makes possible an exclusive activation of the first through flow which is nominally less than the second through flow and accordingly permits a higher accuracy in the metering of smaller through-flow quantities. The drive time is defined as the time duration for the electrical drive of the clocked valve for opening the valve. With the short drive times (relative to the delay of switching in the second flow), small through-flow rates can be controlled with a high precision. Longer drive times lead to the situation that also the second through flow is activated. only by means of the longer drive times are higher through-flow rates made possible which are controllable with adequately high accuracy referred to these large through-flow quantities. In total, the method of the invention permits a precise through-flow control for low as well as for high through flows or through-flow rates.
With respect to fluid substances, it is noted that these include gases, vapors, liquids or other substances having good flow characteristics.
The arrangement according to the invention includes especially a first through-flow control valve having a first nominal through flow and a second or several through-flow control valves having a second nominal through flow. The first nominal through flow is less than the second nominal through flow. The first and the second through-flow control valves can alternatively define a first and an at least second valve stage of an at least two-stage through-flow control valve.
In addition, control means are provided for the time-dependent delayed driving of the at least second through-flow control valve or of the at least second valve stage relative to the first through-flow control valve or the first valve stage.
For low pulse-duty factors, that is, for relatively short opening durations of a through-flow control valve, the time-dependent delay makes possible the exclusive activation of the smaller of the two nominal through flows, namely, that having the first (smaller) through flow. In this way, a small quantity meterability is achieved which is significantly improved compared to the state of the art. Starting at a specific pregivable drive time, the larger or, if required, the next larger (second) nominal through flow is connected thereto so that a very large through flow is possible and this very large through flow is the algebraic sum of the two individual nominal through flows. The switching in of the second through flow only takes place for already significant through-flow values of the first valve. For this reason, the invention therefore makes possible a high meterability at low as well as at high through flows.
In addition to an embodiment having two valves or valve stages, it is emphasized that basically also three or several valves or valve stages can be considered. By increasing the number of valves or valve stages, it can be achieved that the jumps or non-uniformities in the through flows, which occur when switching in individual valves, can be minimized.
When used in a tank-venting system, the special advantage is afforded that the relative accuracy with which large as well as small quantities of fuel vapor or fuel gas can be metered varies less over the entire fuel quantity range than in conventional clocked valves. Especially for small amounts, the mixture errors for active tank venting are thereby reduced, that is, when opening the tank-venting valve in a controlled driven manner.
In a first embodiment, it is provided that the second through-flow control valve or the second valve stage has a delay element by means of which a time-dependent delayable second switch-on flank can be generated compared to a first switch-on flank of the first through-flow control valve or the first valve stage. The delay can, for example, be realized by means of an electrical delay circuit utilizing a relay, which is delayed in time corresponding to the switch-on flank. A hydraulic valve or the like can also be used. In this embodiment, the two through-flow control valves or the two valve stages are advantageously driven by means of only a single control signal whereby the number of control lines is reduced. The control signal is preferably transmitted via an electrical or hydraulic control line or the like to the valves or valve stages.
According to a second embodiment, the first through-flow control valve or the first valve stage can be driven by means of a first control signal and the second through-flow control valve or the second valve stage can be controlled by a second control signal which can be delayed in time with respect to the first control signal. With this embodiment, known through-flow control valves can be used in the realization and only the control unit needs to be exchanged.
In an advantageous embodiment, it is provided that the two through-flow control valves or the two valve stages have respective separate electric drive coils which can be driven separately. This makes possible a technically relatively simple independent control of the two valves whereby costs are reduced.
The arrangement according to the invention can be used in a tank-venting system of an internal combustion engine having a charger mounted in the intake manifold. Fuel vapors escaping from the fuel tank can be introduced into the intake manifold at a first inlet location arranged behind the charger, with this first inlet location being provided on the intake manifold. According to the invention, a second inlet location for introducing fuel vapor is provided. This second inlet location is provided in a region of the intake manifold arranged forward of the charger. Especially at high engine loads or rpms (especially for an active turbocharger), the regeneration of the fuel vapor and fuel gas is thereby considerably facilitated.
A corresponding two-stage or multiple-stage through-flow control valve (especially a tank-venting valve of an internal combustion engine having a fuel supply tank) includes a delay element for generating a time-dependent delayable switch-on flank. The delay element is arranged at the valve or valve stages with the higher nominal through flow. With the arrangement of the delay element at this valve, the number of required control lines can be reduced for the reasons already mentioned herein.
The control unit, which is likewise suggested in accordance with the invention, is for operating such an arrangement and includes a signal generator in a first embodiment. This signal generator is for making available a control signal, which can be pulsewidth modulated, for driving the two through-flow control valves or the two valve stages. Such a control unit is suitable to operate a through-flow control valve wherein the required delay circuit is already present.
According to a second embodiment, the control apparatus includes a signal generator device for generating a first control signal for driving a first through-flow control valve or the first through-flow control valve stage as well as a second control signal for controlling the second through-flow control valve or the second valve stage. The control apparatus also includes an electrical switching device for generating a time-dependent delay of the second control signal relative to the first control signal. For this purpose, conventional through-flow control valves can be used.
The time-dependent delay between driving the two through-flow control valves or valve stages preferably lies in the range of approximately 10 to 50 milliseconds.
It is emphasized that, in contrast to the two-stage tank-venting valves (which are known from the prior art and have three connecting lines, two control lines plus a ground line), the first embodiment according to the invention has only two lines and these are a control line and a ground line. In this way, costs for a second control line are saved and, in addition, the weight of the vehicle is reduced. Furthermore, a second output stage of the control apparatus is unnecessary because only a single control signal need be generated. On the other hand, only costs for the above-mentioned delay circuit need be expended.